A field test for the assessment of faecal contamination of potable water

A simple, sensitive, rapid, inexpensive paper strip impregnated with Salmonella/E. coli medium (SEM) was formulated, and placed in a test tube. When potable water of 10 ml was added to the test tube it detected the faecal contamination of water samples within 16–48 h when incubated at room temperature from 20 to 35 °C. The positive results were indicated when the medium turned black (hydrogen sulfide production) for the presence of Salmonella sp. and/or the formation of a red ring (free indole from tryptophan) when a few drops of Kovac's reagent was added for the presence of coliform bacteria (E. coli). More than 600 water samples were tested with the new test (SEM) and results showed 99% agreement with that of the standard most probable number (MPN) coliform test and also proved highly successful in the field when it was employed to detect both Salmonella and E. coli. Different water testing laboratories involved in a water quality monitoring programme and governmental agencies evaluated the test media and reported that the test was user friendly, reliable and simple to perform in the field and will be especially useful for screening of both urban and rural water supplies for routine monitoring of bacteriological contamination.